Bring a large pan of salted water to the boil and cook the penne according to the package instructions. Add the broccoli for the final two minutes of cooking. Drain well, run under cold water and set aside.

For the sauce, melt the butter in a saucepan and stir in the flour. Cook for three minutes over a medium heat, stirring constantly. Gradually add in the milk and stir until smooth, then simmer for 10 minutes.

Add the grated nutmeg, if using, along with the stock and crème fraîche.

Simmer for 3-4 minutes until thickened, stirring occasionally. Season well and add the lemon juice.

Stir in the penne, cooked chicken and broccoli florets until completely coated.

Transfer to the baking dish, cover with foil and bake for 20-25 minutes until the edges are bubbling. Divide amongst warmed plates and serve immediately.